public float freq = 5;

private float unit;
private float x, y;

private void Start()
{
	x = transform.position.x;
    y = transform.position.y;
}

void Update()
{
    x = unit * Mathf.Cos(Time.time * freq);
    y = unit * Mathf.Sin(Time.time * freq);

    transform.position = new Vector3(x, y);

    unit += (freq / 10) * Time.deltaTime;
}